The present invention relates to a cylinder head gasket to be disposed between two members such as a cylinder head and a cylinder block for sealing therebetween. More specifically, the present invention relates to a cylinder head gasket including one metal plate with a coating layer of paint where a surface pressure is generated.
When a joint portion between a cylinder head and a cylinder block (cylinder body) in an automobile engine is sealed, a cylinder head gasket is placed between the two members for sealing combustion gas or cooling water, etc.
A configuration of the cylinder head gasket has been shifted from a laminated type formed of a plurality of laminated metal plates to a simple structure type in which a cylinder head gasket is formed of a single sheet of metal to meet demands for reducing a weight of an engine and a manufacturing cost. In the cylinder head gasket formed of a single sheet, a material for the plate is limited. As a result, it is difficult to provide a bead, a grommet, or a shim used as sealing means in the laminated type formed of a plurality of metal plates. It is also difficult to overlap the sealing means.
Accordingly, in the simple structure formed of a single sheet, the sealing means is limited in a few varieties and a small quantity, and it is necessary to use simplified sealing means. Further, an area for the sealing means has been decreased as a size of an engine has been reduced.
As shown in FIG. 15, a cylinder head gasket 1 is formed according to a shape of an engine member such as a cylinder block, and has cylinder bores 2, liquid holes 3 for circulating cooling water or engine oil, and bolt holes 4 for inserting bolts. Sealing means 12 and 13 such as a folded portion and a bead are provided for each bore or hole for sealing.
Even in the same gasket for sealing the same engine member, it is necessary to provide different sealing performances according to types of the bores. For the cylinder bore, it is necessary to seal high-temperature and high-pressure combustion gas. On the other hand, for the liquid hole, it is necessary to seal relatively low-temperature and low-pressure liquid.
Also, due to a structure of the engine, there is a difference in a surface pressure between the cylinder bore surrounded by the bolt holes and the liquid hole provided outside the bolt holes and having one sided force applied by the fastening bolt.
In order to provide the different sealing performances, the folded portions 12 are provided for the cylinder bores 2 to seal the high-heat and high-pressure gas inside the cylinder, and the half beads 13 are provided for the liquid holes 3.
When the folded portion is provided for sealing the cylinder bore, the surface pressure is concentrated at the folded portion. Therefore, an engine member made of relatively soft aluminum alloy may be damaged, so that the sealing performance is deteriorated at a damaged area. It is possible to provide an elastic rubber coating for improving compatibility of a gasket with an engine member abutting against the gasket. However, when the elastic rubber coating is used, it is difficult to generate and maintain a large surface pressure. Further, a portion of the elastic coating covering the folded portion tends to creep and wear after a long term due to a large surface pressure generated by the folded portion. The elastic coating also tends to be deteriorated easily by heat and pressure of the gas inside the cylinder, resulting in torque down, i.e. a decrease in the sealing surface pressure. As a result, it is difficult to maintain the sealing performance for a long time.
When a shim is provided for adjusting a distribution of the surface pressure around the folded portion, it is difficult to fine adjustment of the surface pressure due to a limitation of adjusting a thickness of the shim, and it takes a long tedious process to form the shim. In addition, when the shim is formed at an end portion of the folded portion or a depression formed with coining to adjust a level difference, it is necessary to perform the coining and provide an accurate mold, thereby increasing a cost.
In view of the problems described above, the present invention has been made, and an object of the invention is to provide a cylinder head gasket formed of a single metal plate for sealing a joint surface between two members such as a cylinder head and a cylinder block of an engine, wherein it is possible to generate and maintain appropriate distributions of surface pressures around a cylinder bore and a liquid hole, thereby obtaining good sealing performance and good durability.
Another object of the invention is to provide a cylinder head gasket in which it is possible to adjust the distributions of the surface pressures around the cylinder bore and the liquid hole to meet different sealing performances, respectively.
Further objects and advantages of the invention will be apparent from the following description of the invention.